The present invention pertains to compatible blends containing a relatively high molecular weight polyol and a relatively low molecular weight polyol containing primary hydroxyl groups.
Polyurethane articles, commonly formed by the RIM (Reaction Injection Molding) process, are polymer products resulting from the reaction of liquid polyol mixtures and liquid polyisocyanates. These rapid polymerization processes commonly employ a blend of low equivalent weight glycols such as ethylene glycol or 1,4 butanediol and primary hydroxyl terminated high molecular weight polyether polyols. Such blends of ethylene glycol and a 5000 mol. wt. primary capped polyether polyol are incompatible fluids that tend to separate into layers on standing.
Recognition of this effect dictates that these blends should be constantly agitated to avoid a misformulation by the separation of components or in some cases, additively, a tendency for catalyst migration occurs in these blends that also contain a heavy metal catalyst such as organotin compound. Further, in certain instances, agitation of these fluid blends during storage or shipment or transfer is not practical or may be difficult.
U.S. Pat. No. 3,929,730 teaches the use of 1,4 butanediol as a "chain extender" that is blended with high molecular weight polyols (about 2000 m.w. or greater) to prepare polyurethane compositions. However, 1,4 butane diol is insoluble in polyol at the concentration usually employed (see lines 60-70, col. 1 and part C or claim 1). A sufficient amount of phenylenediethanolamine is used to render the mixture soluble in the polyol.
U.S. Pat. No. 3,993,576 teaches a composition resistant to phase separations (in the mixture of high mol. wt. polyols and low mol. wt. polyols) by the addition of a "solubilizer", a derivative of butylene glycol or propylene glycol.
U.S. Pat. No. 4,008,185 teaches the use of urea as a catalytic modifier for preparing rapid-setting polyurethanes by reacting a polyol free from nitrogen groups or a mixture of such polyols having from 2 to about 8 hydroxyl groups per molecule and an OH equivalent weight from about 30 to about 500 and an aromatic polyisocyanate. However, urea failed to catalyze the reaction of polyols having an equivalent weight of 500 or higher with aromatic isocyanates.
The solubilizing agent in U.S. Pat. No. 3,929,730 is a substituted ethanolamine and the solubilizing agent in U.S. Pat. No. 3,993,576 is a polyol derivative of butylene or propylene glycol. We disclose solubilizing agents within the group of urea and/or substituted urea's that contain no hydroxyl groups or other active hydrogen groups capable of reacting with isocyanates under conventional RIM reaction conditions. Such compounds as diethanol urea dissolved in ethylene glycol failed to compatibilize blends of ethylene glycol and high molecular weight primary hydroxyl terminated polyols compared to the use of urea. We find that the hydrogen atoms bonded to the nitrogen atoms in ureas or substituted urea's exhibit no significant reactivity with isocyanates under RIM reaction conditions. The substituted urea's, further, must also be free of reactive groups capable of reacting with hydroxyls or amines.
We have discovered that the addition of a minor amount of urea and/or substituted urea's to the incompatible polyol blends renders these mixtures into a compatible or single phase liquid. These blends of low equivalent weight glycol and high equivalent weight primary capped polyol that have been compatibilized by the addition of minor amounts of urea and/or substituted urea's and may also contain an organotin compound as a catlyst show no significant loss in reactivity after standing.
We have further discovered that such urea and/or substituted urea compatibilized blends of low equivalent weight polyols such as ethylene glycol and/or 1,4 butane diol and high molecular weight primary capped polyols (equivalent weight of about 1000 or greater) where the high mol. wt. polyol is the major weight function of the hydroxyl components is RIM reactive in the absence of any organo metal (i.e. Sn carboxylate etc.) or amine catalyst. In other words, the compatibilized polyol blends mentioned above are catalyzed to react with polyisocyanates by the presence of urea and selected substituted ureas as the sole catalyst.